#include <stdio.h>

int main(void)
{
    char input[30] = "This is a test message.\n";
    char output[30];
    int length = 25;
    asm volatile ("cld\n\t"
    "rep movsb"
    :
    : "S"(input), "D"(output), "c"(length)
    : "memory");
    printf("%s", output);
    return 0;
}